A perfluoroelastomer of tetrafluoroethylene (TFE)-perfluorovinyl ethers are widely used in fields such as automobile industries, semiconductor industries and chemical industries as seal materials such as O-ring, a stem seal and a shaft seal, which are utilized under severe environments, in viewpoints of showing its prominent chemical resistance, solvent resistance and heat resistance.
These perfluoroelastomer seal materials are usually prepared by press vulcanization after mixing a perfluoroelastomer with a vulcanizer, a filler and various additives by a roll etc. Thereafter, it is general to further apply the second vulcanization for enhancing performance. However, a molecular chain of a perfluoroelastomer, which is a polymer with a high molecular weight, is cut out by stress received at processing and heating at the second vulcanization, and as a result, a component having a low molecular weight and an uncrosslinked polymer are generated. A seal material comprising a perfluoroelastomer containing a great amount of these component having a low molecular weight and uncrosslinked polymer adheres firmly to a part of the other material where the seal material is applied at use, which makes desorption of the seal material difficult, and has bad influence on the operation of a device at dynamic portions. Further, there is a problem such as causing stain, corrosion and color change on the other material by the component having a low molecular weight and the uncrosslinked polymer which bleed out. Since the component having a low molecular weight and uncrosslinked polymer are generated not only at polymerization but also in a step of processing, the problem can not be improved by decreasing the component having a low molecular weight etc due to improvement of a polymerization method, thus, it is necessary to remove the component having a low molecular weight after the process.
As a process for decreasing outgas from a seal material made of a fluorine rubber and inhibiting contamination of a vacuum chamber applied with the seal material, a process for contacting a crosslinked fluorine rubber with a solvent such as water is disclosed (for example, see JP-A-6-107803). However, since a perfluoroelastomer does not swell sufficiently with the solvent described in the publication, the component having a low molecular weight generated at processing etc can not be sufficiently removed from the inside of the molded article. As a result, firm adhesion and stain of the seal material can not be inhibited.
Also, as a treatment of a rubber core material of O-ring having a composite structure for improvement in vacuum performance, a process for removing outgas by a supercritical extraction treatment is disclosed (for example, see JP-A-10-38089 or JP-A-2000-55204). However, these processes do not directly improve adhesivity of a rubber substrate which is a base.
Therefore, the process for removing the component having a low molecular weight etc which causes increase of the adhesion strength, and stain, corrosion and color change of the part contacting with a seal material, and a perfluoroelastomer seal material in which the component having a low molecular weight has removed is not existed under the current situation.
The present invention provides a perfluoroelastomer seal material improved in adhesion strength to the material of the other end, and stain, corrosion and color change of the contact surface, wherein a rate of weight decrease is at most 1% by weight measured under particular conditions.